Does PHP copy object data structures when I pass objects to functions or methods?

I know there's the option to pass开发者_开发问答 a value by reference, simply by writing something like

function foo(&$bar) {...}

But from Objective-C I'm used to believe that objects are always passed by reference (since the variables referencing them are just pointers whose values are just a memory address). Only sctructures and primitives would have to explicitely be passed by reference.

How's that going on in PHP? Must I be sure to put that address operator & into every parameter to enhance performance when passing objects?

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Only in versions prior to PHP5. In PHP5 objects are always passed by reference.

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PHP5 passes object by reference. To pass them by value you can use the keyword clone.